「ふげん」原子炉解体への水中レーザ切断技術の実用化に向けた取り組み

Efforts toward the practical application of underwater laser cutting for the dismantling of the Fugen nuclear reactor

岩井 紘基 ; 古旗 壮一朗; 香田 有哉 

Iwai, Hiroki; Furuhata, Soichiro; Koda, Yuya

新型転換炉原型炉ふげんの原子炉解体における炉心構造物の切断工法として、水中レーザ切断技術の適用性について報告する。ふげん炉心部は大型ステンレス鋼製容器内に多数のジルコニウム合金製配管を有する複雑かつ狭隘な構造である。炉心構造物は長期運転に伴い放射化しており、内部は高線量環境となっていることから、水中遠隔解体を基本方針としている。レーザを含めた複数工法を対象に要素試験を実施し、加工性能及び特性を比較評価した。その結果、レーザ切断は、遠隔操作適用性、廃棄物低減及び工程合理化の観点から最も優れたバランスを示したため、基幹切断工法として選定した。さらに、実機適用に向けて小型切断ヘッド開発、遠隔制御、視認性確保及び粉じん低減対策に関する実証試験を実施し、適用に向けた技術的見通しを得た。

This paper presents the applicability of underwater laser cutting technology as a cutting method for reactor core components in the decommissioning of the Advanced Thermal Reactor (ATR) Fugen. The reactor core consists of a complex and highly congested structure containing numerous zirconium-alloy tubes inside a large stainless-steel vessel. Because the core structures have become highly activated after long-term operation, resulting in a high-radiation environment, underwater remote dismantling has been adopted as the basic dismantling strategy. Elemental tests were conducted on several candidate cutting methods, including laser cutting, and their cutting performance and operational characteristics were comparatively evaluated. The results showed that laser cutting provides the best overall balance among the evaluated methods in terms of suitability for remote operation, reduction of secondary waste, and improvement of dismantling efficiency. Consequently, laser cutting was selected as the primary cutting method for dismantling the reactor core structures. Furthermore, demonstration tests have been carried out to support practical applications, including the development of a compact cutting head, measures for maintaining visibility and mitigating dust and water turbidity, and improvements in remote-control performance. Through these studies, favorable prospects for the practical application of underwater laser cutting technology to the dismantling of reactor core structures have been obtained.